Instrument for the removal of a bone insert and corresponding method

ABSTRACT

The invention relates to an instrument and a corresponding surgical method for the removal of a bone insert, for example for a shoulder prosthesis. The instrument is of the type comprising:
         a stem-like body ( 40 ) extending along a longitudinal axis (x-x) and provided with a proximal grip and a distal operating head ( 15 ) slidably associated with the stem-like body ( 40 ) for movement towards and away from each other;   a cutting element ( 30 ) inside said operating head; and   an end tip ( 16 ) protruding coaxially from said operating head. The following is also provided:   a pushing mechanism ( 8 ), inserted inside said operating head and acting on said cutting element so as to displace it angularly from a rest position, where it is concealingly housed inside said end tip, to an operative position where it projects through a side opening in the end tip; said cutting element having an end extending substantially in a direction transverse to said longitudinal axis when in the operative position.

The present invention relates to an instrument for the removal of a boneinsert intended, for example, for a reverse or anatomical shoulderprosthesis.

The principles of the present invention are applicable to variousoperational requirements, but the description which follows is providedwith more specific reference to the treatment of different degrees oferosion of the glenoid cavity following a trauma or a pathologyaffecting the shoulder, without this however implying any limitation ofthe Applicant's rights.

From the content of the attached claims it will become clear that thescope of protection of the present invention extends to surgicalapplications intended for the removal of bone inserts in areas of theskeleton not limited to the example of the humeral head.

FIELD OF APPLICATION

As is well known, the humerus is a long bone of the upper limbs and isthe main element in the skeletal structure of the arm since the otherlong bones of the upper limbs, namely the radius and the ulna, areanatomically speaking considered to form part of the forearm.

The humerus comprises a long body, called the diaphysis, and twoopposite ends called the epiphyses, i.e. proximal epiphysis and distalepiphysis. The proximal epiphysis is articulated with the scapulaforming a scapulo-humeral articulation, while the distal epiphysis isarticulated with the two bones of the forearm, i.e. the radius and theulna.

The head of the humerus, namely the proximal epiphysis, has a largesmooth hemispherical surface which is lined with a cartilage and isseated in a glenoid cavity of the scapula. The head is bounded at thebottom by the both anatomical and surgical neck of the bone.

It should also be noted that at the bottom of the anatomical neck, inthe front part of the bone, there is a forwards facing protuberanceknown as the lesser tubercle (also called trochin) inside which asubscapularis muscle is inserted. At the top and laterally with respectto the lesser tubercle there is the greater tubercle (called trochiter)which, with its three faces, allows the insertion of other muscles ofthe so-called rotator cuff.

Over and above these anatomical details, for the purposes of the presentinvention, it should be pointed out that the glenohumeral joint allows alarge degree of movement of the upper limb necessarily to the detrimentof the stability. Thus the anatomical system must ensure the rightbalance between mobility and stability, something which makes theglenohumeral joint prone to clinical instability. The instability is apathological condition which is manifested in the form of acute painassociated with an excessive displacement of the humeral head inside theglenoid cavity during the active movement of the shoulder.

Static and dynamic factors play a complex and cooperative part inmaintaining the articular stability. In-depth studies have establishedthat there exists a certain instability factor when erosions are presentin the glenoid cavity.

More particularly, it has been established that there essentially threedifferent morphologies of the glenoid cavity, which may be classified asfollows:

-   -   concave morphologies, which represent about 54% of the cases and        are characterized by a small degree of central wear and a        central dome;    -   biconcave morphologies, which represent 42% of the cases and are        characterized by a rear peripheral wear with more or less        partial rear dislocation;    -   retroverse morphologies, which are less common and take the form        of an excessive retroversion of the glenoid cavity by more than        25°, normally of dysplastic origin.

Studies carried out on patients with arthrosis have showed that inglenoid cavities with non-concentric arthropy and rear erosion there isa high complication rate which adversely affects the stability andbiomechanics of the articulation.

However, these problems may be solved surgically by attempting torestore the stability and biomechanics of the articulation so as toeliminate the pain from which the patient is suffering.

In order to restore the correct stability and biomechanics parameters aswell as achieve renewed mobility with elimination of the pain, a reverseor anatomical total prosthesis, as appropriate, may be convenientlyused.

A prosthesis is an artificial joint or articulation, made of metal orplastic, which resembles in form the glenohumeral articulation.

The prostheses normally comprise both a humeral prosthetic component anda glenoid component and, in so-called reverse prostheses, thesecomponents are substantially reversed compared to an anatomical totalprosthesis.

PRIOR ART

In order to restore optimally the biomechanics of the articulation, theerosion and the angle of the glenoid cavity must also be rectified insome way. One of the operative techniques envisages the possibilities ofusing bone implants instead of metal implants.

These implants, in the case of a first implant, may be obtained from thehead of the humerus which must in any case undergo resection in order tomake space for the humeral component of the prosthesis.

For example, in the case of reverse prostheses, in which there is aglenoid component terminating in a concave articular surface, thepresence of a bone insert between the glenoid cavity and the prosthesisis envisaged.

A surgical technique which envisages the removal and implant of a boneinsert is for example described in detail in French patent applicationNo. 2,916,961 in the name of Tornier.

Although advantageous in various respects and substantially meetingneeds, the surgical technique described in that document has a majordrawback relating to the operating step where a bone insert is removedfrom the head of the humerus.

The bone insert in question, which is removed from the head of thehumerus, is used to complete the structure of the prosthesis on theglenoid cavity side since it is arranged between the convex end portionof the glenoid component of the prosthesis and a seat specially preparedinside the articular cavity so as to form a bone callus forconsolidating in situ the prosthesis.

The insert is suitably removed from the head of the humerus which, asmentioned, must in any case undergo resection by the surgeon in order toseat the concave humeral component of the reverse prosthesis, whileensuring compatibility and preventing any risk of rejection.

The step of core-boring or drilling the bone insert and subsequentremoval thereof by means of a lateral cut performed in the head of thehumerus are carried out before the same bone insert may be attached toits prosthesis component.

This means that the bone insert must be handled after its removal ormust in any case be placed to one side pending completion of the othersurgical steps necessary for preparing the glenoid cavity, with thepotential risk of bacterial contamination.

Moreover, the operating steps for boring and removal of the insert areobjectively complex and demanding for the surgeon and involve the use ofa large number of specific instruments which also result in the removalof a quantity of bone material far greater than that which would bestrictly necessary for completion of the steps for preparing insertionof the prosthesis.

Finally, it must also be commented that the surgical technique proposedby the prior art for removal of the bone insert is relativelyinefficient from the point of view of the sequence of operating stepswhich are necessary for completion of the operation.

The present invention aims to overcome all these drawbacks byconsidering the technical problem of how to provide an instrument andcorresponding surgical method able to allow the removal of a bone insertin a simpler and more efficient manner compared to the known solutions,while ensuring at the same time completely sterile handling of theinsert.

SUMMARY OF THE INVENTION

The proposed solution forming the basis of the present invention is thatof extracting or removing the bone insert to be removed by alreadyassociating it or attaching it to a portion of the relevant prosthesiscomponent.

This basic idea also involves modification of the method of removal ofthe bone insert compared to the sequence of steps envisaged by the priorart.

On the basis of this proposed solution, the scope of which isunderstandably broader than that expressly implied with reference to theexample of the anatomical or reverse shoulder prosthesis, theaforementioned technical problem is solved by an instrument for removalof a bone insert, for example for a shoulder prosthesis, of the typecomprising:

-   -   a stem-like body extending along a longitudinal axis (x-x) and        provided with a proximal grip and a distal operating head;    -   a cutting element inside said operating head; and    -   an end tip projecting coaxially from said operating head,        characterized in that it comprises further:    -   a pushing mechanism, inserted inside said operating head and        acting on said cutting element so as to displace it angularly        from a rest position, where it is concealingly housed inside        said end tip, to an operative position where it projects through        a side opening in the end tip; said cutting element having an        end extending substantially in a direction transverse to said        longitudinal axis when in the operative position.

Advantageously, the cutting element is curved or has the form of acircle arc and comprises a widened proximal portion slidable inside aguide of matching shape formed in the operating head and a tapered endportion which is angularly movable between the rest position, where itis concealingly housed inside the end tip of the operating head, and theoperative position, where it extends transversely projecting relative tothe longitudinal axis.

The operating head has an essentially cylindrical shape and comprises acircular-rim guide inside which the cutting element is movably guided.

The distal portion of the operating head is slightly concave, while theend tip has a frustoconical form with a base diameter smaller than thediameter of the operating head and projecting coaxially with thelongitudinal axis from the distal portion.

It should be noted that the pushing mechanism also comprises a resilientelement which constantly biases said cutting element towards said restposition.

Moreover, the pushing mechanism comprises a distal end of the stemacting on the cutting element.

In greater detail, the pushing mechanism is such that the stem isslidable inside said operating head with a predefined longitudinalstroke so that its distal end acts on said cutting element against theaction of spring-loaded means; sliding of the stem is obtained by meansof an advancing and retracting movement engaged on a perimetral portion.

The distal end of the stem has a circular cross-section and diametersmaller than the internal diameter of the operating head, while thespring-loaded means consist of a spring wound around the distal end ofthe stem.

The spring extends resiliently inside a variable-extension, cylindrical,annular gap which is defined between an inner edge of the operating headand an edge formed by the smaller diameter of the distal end of thestem.

The technical problem is also solved by a method for removing a boneinsert intended, for example, for a shoulder prosthesis, of the typecomprising the steps of:

-   -   forming a hole of predefined diameter inside a bone portion from        which said insert is to be removed;    -   inserting inside said hole an operating end of an instrument        provided with a cutting element;    -   said cutting element being movably guided from a rest position,        where it is concealingly housed inside said end, to an operative        position, where it projects through a side opening in the said        end, transversely relative to a longitudinal axis of the        instrument;    -   deep-cutting a base of said insert by rotating said instrument        through 360 degrees;    -   removing the instrument from said hole;    -   inserting and fixing a pin element inside said hole;    -   perimetrally milling an insert of predefined diameter by        centering a milling cutter on said pin element;    -   removing the insert and the pin element attached thereto.

The characteristic features and advantages of the instrument and theassociated method according to the invention will emerge from thedescription of a non-limiting example of embodiment provided withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic cross-sectional view of a reverse totalshoulder prosthesis according to the prior art;

FIG. 2 shows a diagrammatic perspective view of a bone portion to whichthe method of the present invention is applied, for example the head ofa humerus;

FIG. 2A is a diagrammatic longitudinally sectioned view of the boneportion according to FIG. 2;

FIG. 3 shows a diagrammatic side view of an instrument provided inaccordance with the present invention during approach towards a boneportion to be treated;

FIG. 4 shows a perspective picture view showing the instrument of thepresent invention before an operating step;

FIG. 5 shows a diagrammatic cross-sectioned side view of the instrumentaccording to the present invention at the start of an operating step;

FIG. 6 shows a diagrammatic cross-sectioned side view, similar to thatof FIG. 5, in which the instrument according to the present invention isat the start of an operating step;

FIG. 7 shows a perspective picture view showing a portion of theinstrument according to the invention during its operating step;

FIG. 8 shows a diagrammatic cross-sectioned side view of the instrumentaccording to FIG. 7 during operation;

FIG. 9 shows a perspective view of a detail of the instrument accordingto the invention;

FIG. 10 shows a longitudinally sectioned view of a detail of the boneaccording to FIG. 2, in which a deep cut has been made using theinstrument according to the invention;

FIG. 11 shows a diagrammatic perspective view of a detail of the boneaccording to FIG. 2 in which a prosthesis component is about to beinserted;

FIG. 12 shows a longitudinally sectioned view in which the prosthesisportion according to FIG. 11 has been inserted in the bone portionaccording to FIG. 2;

FIG. 13 shows a partially sectioned diagrammatic view of the boneportion according to FIG. 2 undergoing successive operating steps of themethod according to the invention;

FIGS. 14 and 15 show respective partially sectioned diagrammatic viewsof operating steps of the method according to the invention;

FIG. 16 is a perspective picture view of the example shown in FIG. 15from a different view point;

FIG. 17 shows laterally sectioned view of a detail of the bone portionaccording to FIG. 2 practically at the end of the operating steps of themethod according to the invention;

FIG. 18 is a perspective picture view of extraction and removal of aninsert performed using the instrument and the method according to thepresent invention.

DETAILED DESCRIPTION

As already mentioned above, the instrument and the removal methodaccording to the present invention, which will be described in detailbelow, are applicable to the removal of any bone insert, which couldalso be situated in the femoral iliac zone, without this involving anylimitation of the Applicant's rights.

However, the attached drawings show in diagrammatic form the headportion of a bone along the human skeleton, for example the head of ahumerus, as an example application of the instrument and the methodaccording to the invention.

The removal method is described below with reference to a surgicaltechnique applied to the implantation of a reverse total shoulderprosthesis shown in FIG. 1, but only by way of a non-limiting exampleand for the purpose of simplification of description of the invention.

FIG. 1 shows in diagrammatic form a reverse total shoulder prosthesis 1with an already known structure.

In the sector of total shoulder prostheses, reverse prostheses comprise,on one side, a glenoid component associated with the glenoid cavity G ofa scapula S of a patient and terminating in a convex articular surface11A and, on the other side, a component integrated in the humerus Hdefining a concave articular surface 22A; these two articular surfaces11A, 22A, cooperating with each other, recreate the shoulder joint.

FIG. 1 shows a shoulder prosthesis 1 comprising a glenoid component orglenoid cavity and a humeral component, indicated by the numbers 10 and20, respectively, and situated in the scapula S and in the humerus H ofa patient. The glenoid component 10 comprises a head 11 which has, onthe opposite side to the glenoid cavity G of the scapula S, an articularconvex face 11A with a generally semispherical form and, on the sidedirected towards the glenoid cavity G of the scapula S, a flat face 11B.In the illustrative example shown in the figures, the face 11B isgenerally flat, but it may also have a more elaborate geometry and befor example substantially concave or convex.

The glenoid component 10 further comprises an anchoring stem 12 whichextends transversely with respect to the projecting face 11B, in theopposite direction to the face 11A, and the free end of which is firmlyanchored in the glenoid cavity G, thus ensuring joining of the glenoidcomponent to the side of the scapula S. The shank 12 may be externallythreaded or, in general, have a surface which favors anchoring. A boneinsert 2 is arranged between the face 11B of the glenoid portion 10 ofthe prosthesis and the glenoid cavity G of the scapula S, said inserthaving a substantially cylindrical external shape, with a circular base,the external diameter of which is substantially the same as the diameterof the head 11.

The bone implant 2 to be associated with the glenoid component of theprosthesis is removed from the upper epiphysis of the humerus of theshoulder of the same patient. In this way the risk of rejection, poorbiocompatibility or the potential transmission of diseases or infectionsis reduced.

Moreover, in this way advantageously also resection and forming of thehead of the humerus which is suitable for engagement of the otherhumeral component of the reverse total prosthesis is obtained.

The humeral component 20 of the reverse prosthesis comprises a medullarystem 21 intended to be inserted inside the medullary cavity M of thehumerus H. At the top end the stem 21 widens into a head 22 which has onits side opposite to the shank 21 a concave articular surface 22A with asemispherical form having a radius substantially the same as that of theconvex surface 11A. When the prosthesis 1 is implanted, as shown in FIG.1, the surfaces 11A and 22A are directed in contact against each other,allowing the various movements required by the shoulder.

Owing to the presence of the implant 2, the face 11A is situated at apredefined distance from the glenoid surface G and this arrangement isreferred to, in the technical jargon of the sector, as induced“lateralization”. Advantageously, the lateralization of the glenoidcomponent of the prosthesis also induces an increase in the musculartension of the rotator cuff. The glenoid and humeral prostheticcomponents are thus stabilized and therefore benefit from improvedrelative rotation and a better mobility without any longer the risk of ashoulder dislocation. Furthermore, the geometric centre of articulationof the prosthesis is situated correctly in the glenoid cavity.

Advantageously, according to the present invention, the surgical methodand the instrument described here allow easier removal of the boneinsert 2, for example both for a reverse prosthesis 1 of the shoulder,such as that described above, and for other types of operations which inany case require the removal of bone inserts from a patient.

The steps of the surgical method developed by the Applicant may beeasily understood from the sequence shown in FIG. 2 onwards.

The description which follows does not intend to describe all the stepsinvolved in the surgical treatment for removal of the bone insert 2, butonly those steps which are most important and relevant to thedescription of the invention; therefore, detailed explanations as to howthe patient is positioned or how the head of the humerus or the glenoidcavity are surgically exposed will be omitted.

For the purposes of the present invention, the humeral epiphysis 3undergoes firstly a milling operation to define a concave recess 4 whichhas substantially the shape of a spherical cup.

A central hole 5 of predefined diameter, in particular a hole with afrustoconical shape, is formed in the bottom of this recess 4.

Obviously, the person skilled in the art will understand that the shapeof the hole 5 may be cylindrical if necessary.

The milling resection means for performing a resection in the humeralepiphysis and defining the concave recess 4 as well as the drillingmeans for centrally boring the hole 5 are of the conventional type andmay be used in cooperation with a centering or guide stem (not shown inthat conventional) which helps define the direction of application ofthese means for forming the hole 5 centered in the recess 4.

Similarly, the person skilled in the art will understand that the stepsfor forming the recess 4 and the hole 5 could also be reversed with theformation of the hole 5 which may precede the removal of the bonematerial from the humeral epiphysis until the concave recess 4 isobtained.

In any case, at the end of these first operating steps, the head of thehumerus has a receiving seat 6 formed by the assembly of the hole 5 andconcave recess 4 which is subsequently intended to house a pin element25 visible in FIGS. 11 and 12. This pin element 25 comprises a flange23, with shape matching that of the concave recess 4, and a pin 24projecting centrally and intended to be inserted inside the hole 5.

Preferably the pin 24 has circular and longitudinal grooves for betteranchoring of the pin element 25 inside the hole 5 and stabilization ofthe flange 23 inside the recess 4 of the receiving seat 6.

In accordance with the present invention, an instrument 9 is brought upclose with its operating end 15 so that it may be inserted inside theseat 6, as shown in FIG. 3.

The internal structure of the instrument 9 can be seen from thecross-sectional view shown in FIGS. 4, 5, 6 and 8.

The instrument 9 comprises a stem-like body 40 extending along alongitudinal axis (x-x) and provided with a proximal grip and a distaloperating head 15. The distal operating head is slidably mounted on oneend of the stem 40 between a rest position and an operative position.

The operating head 15 is provided internally with a cutting element 30,in particular a blade having a predefined constant lateral thickness.

An end tip 16 projects coaxially from said operating head 15 and forms akind of laterally open frustoconical bit.

The operating head 15 has internally a pushing mechanism 8 for acting onthe cutting element 30 so as to displace it angularly from a restposition, where it is concealingly housed inside the end tip 16, and anoperative position where it projects through a side opening 27 in theend tip.

The cutting element 30 has a blade 31 extending substantially in adirection transverse to said longitudinal axis x-x when it is in theoperative position.

As is clearly shown in FIGS. 6, 7 and 8, when the blade 31 of thecutting element 30 starts to emerge through the side opening 27 of theend tip 16 it also starts to perform its incision function in the spongypart of the bone to be cut. As the end 31 performs its action, a cut 7is formed and, following rotation of the instrument 9 through 360°, thiscut assumes an essentially circular form.

The cutting element 30 is curved, essentially in the form of asemi-circle or circle arc, and comprises a widened portion 28, whichextends over most of the circle arc and is slidable inside a guide 18provided in the solid-material portion of the operating head 15, and atapered blade 31, which is angularly movable between said rest position,where it is concealingly housed inside the end tip 16 of the operatinghead 15, and said operative position, where it extends transversely withrespect to the longitudinal axis (x-x) in the manner of a sickle.

The widened proximal portion 28 is slidable inside the circular-rimguide 18 of matching shape formed in the operating head 15, thus movingangularly about a point of instantaneous rotation—diagrammaticallyindicated by O—which is also the centre of the curved cutting element 30and the circular-rim guide 18. A pin 35 is also provided, integral withthe cutting element 30, and extends perpendicularly with respect to theplane in which said cutting element 30 lies, as can be clearly seen inFIG. 9.

A guide slot 33, which is eyelet-shaped, is formed transversely withrespect to the axis x-x on the distal end of the stem and is engaged bythe pin 35 and acts on the said pin during displacement from the restposition to the operative position.

The operating head 15 has an essentially cylindrical shape and surroundsthe pushing mechanism 8 and the distal end portion 8, which ispreferably fork-shaped, of the stem 40.

The solid-material distal portion 39 of the operating head 15 isassociated with the end tip 16 which is substantially the end part of acylindrical shaped lid or cover with a frustoconical end tip 16, whichcovers both the distal end 38 of the stem 40 and the distalsolid-material portion 39 of the operating head 15 so as to be formedintegrally therewith.

A pin 26 is provided projecting laterally from the operating head 15 soas to be snap-engaged by a deformable element formed in the cylindricalcover and visible in FIG. 4.

When the end tip 16 fixed to the operating head of the instrument 9 isinserted inside the hole 5, the distal surface of the operating head 15comes into mating contact with the recess 4 of the seat 6 on theepiphysis of the humerus.

The pushing mechanism 8 also comprises a resilient element 34 arrangedbetween the stem 40 and the operating head 15 and constantly biasing thestem 40 and the operating head 15 away from each other and therefore thecutting element 30 towards said rest position.

The side opening 27 in the end tip 16 is an opening extending along theentire longitudinal extension of the end tip, as shown in FIG. 7, so asto allow the blade 31 of the cutting element 30 to emerge fully.

The pushing mechanism 8, and in any case the distal end portion 38 ofthe stem 40, is slidable inside the operating head 15 with a predefinedlongitudinal travel. The fork-shaped distal end 38 of the stem 40engages with the pin 35 via the guide slot 33 and therefore forces thecutting element 30 to slide inside its matching seat 18 against theaction of the resilient means 34.

The distal end 38 of the stem 40 has a circular cross-section anddiameter smaller than the internal diameter of the operating head 15 andhas the function of receiving a section of the resilient element 34 andguiding it during the compression and release phase.

By means of the pushing or pressing force applied by the surgeon actingon the grip 19 of the stem 40 the blade 31 may be gradually made toprotrude against the action of the resilient recall means 34, so thatthe resection action occurs gradually with rotation of the instrumentthrough 360°.

Once the blade 31 has completed, acting in the manner of a sickle, theoperations for resection of the deep base of the bone insert 2, thusperforming the circular cut 7, the instrument 9 may be removed,releasing the resilient means which perform their elastic recall action34 recalling the cutting element 30 inside the end tip 16 of theoperating head 15.

In this way, the instrument is free again and may be removed.

The end portion 3 of the bone M which is operated on for removal of theinert 2 has a cross-section as shown in FIG. 10 where a deep base 47 ofthe insert 2 has been defined by means of a circular cut 7.

At this point it is possible to insert the pin element 25—also called“metal back”—which has an engaging portion 24 with perimetral groovesand is inserted by means of an interference fit inside the hole 5 untilthe flange makes bearing contact inside the matching recess 4 of theseat 6, as clearly shown in FIGS. 11 and 12.

The flange 23 has holes for stabilizing bone screws.

Thereafter the method according to the invention envisages successiveterminal operative steps, some of which may be defined as beingoptional.

For example, FIG. 13 shows a guide rod 45 which has a threaded end 44inserted inside the pin element 25.

The pin 24 is internally hollow and has a thread inside which theaforementioned end 44 of the guide rod 45 may be engaged.

This guide rod acts as a guide for a milling cutter 50 provided with anend tool 48 with an essentially circular shape designed to performcore-boring of the insert 2 around the flange 23.

FIG. 15 shows diagrammatically the action performed by the tool 48 ofthe milling cutter 50 on the head of the humerus M.

The perimetral milling or core-boring operation produce a cylindricalcut 43 which penetrates deep as far as the circular cut 7. In this waythe insert 2 is easily resected from the surrounding bone material andmay be easily removed by means of a suitable removal instrument.

The milling cutter 50 is then removed and an extractor 55 with agripping head 54 is used to remove the insert 2 thus cut. As clearlyshown in FIG. 18, the extractor 55 is in turn guided along the guide rod45 which is still fastened to the pin element 25. The gripping head 54is snap-engaged with the flange 23 of the pin element 25 and the insertattached to the pin element 25 may be removed.

More particularly, the extractor 55 of the metal back 25 snap-engagesonto the guide rod 45. The head 54 enters inside the screw holes of theflange 23 of the metal back 25 in order to stabilize the rotationalmovement about the axis of the extractor and therefore allow directionaladjustment of the implant.

The operating steps which allow removal of the bone insert 2 from theportion 3 of bone H may be summarized extremely succinctly as follows:

-   -   forming a hole 5 of predefined diameter inside a bone portion        from which the insert 2 is to be removed;    -   inserting inside the hole 5 the operating end 16 of the        instrument 9 provided with a cutting element 30;    -   the cutting element 30 being movably guided from a rest        position, where it is concealingly housed inside the end tip 16        of the operating head 15, to an operative position, where it        projects through a side opening 27 in the said end tip 16,        transversely with respect to a longitudinal axis x-x of the        instrument 9;    -   deep-cutting a base of the insert 2 by rotating the instrument 9        through 360°, as is clearly shown in FIG. 7;    -   removing the instrument 9 from the hole 5;    -   inserting and fixing a pin element 25 inside said hole 5;    -   perimetrally milling the insert 2 of predefined diameter by        centering a milling cutter 50 on said pin element 25;    -   removing the insert 2 and the pin element 25 attached thereto.

The fact that the seat 6 also comprises the surface recess 4 is entirelyoptional. Obviously, this surface recess 4 may advantageously receivethe flange 23 attached to the pin 25

This flange 23 is integral with the pin 25 and removal of the insert 2is performed by engaging the flange 23 using the extractor 55 which canbe seen in FIGS. 17 and 18.

Once a circular base 47 of the bone insert 2 has been deep-cut, it ismerely required to mill perimetrally the insert using a circular millingcutter circumscribing the flange 23 of the pin element 25 which is fixedto the insert 2 even before the milling operation is performed.

It is entirely clear that, as a result of the instrument and the methodaccording to the present invention, it is possible to reduce and speedup the operating steps designed to remove the bone insert useful forcombining with implanted prostheses.

The removal methods are furthermore less invasive than those proposed bythe prior art and allow most of the bone material to be conserved andused for the insert to be removed.

1. Instrument (9) for the removal of a bone insert, for example for ashoulder prosthesis, of the type comprising: a stem-like body (40)extending along a longitudinal axis (x-x) and provided with a proximalgrip (19); a distal operating head (15) slidably associated with thestem-like body (40) for movement towards and away from each other; acutting element (30) inside said operating head (15); and an end tip(16) projecting coaxially from said operating head (15), characterizedin that it comprises further: a pushing mechanism (8), inserted insidesaid operating head (15) and acting on said cutting element (30) so asto displace it angularly from a rest position, where it is concealinglyhoused inside said end tip (16), to an operative position, where itprojects in a cantilever manner through a side opening (27) in the endtip; said cutting element (30) having a blade (31) extendingsubstantially in a direction transverse to said longitudinal axis (x-x)when in the operative position.
 2. Instrument according to claim 1,characterized in that said cutting element (30) is curved or in the formof a circle arc and comprises a widened proximal portion (28), slidableinside a matching shape guide (18) formed in said operating head (15),and a tapered blade (31) which is angularly movable between said restposition, where it is concealingly housed inside the end tip (16) of theoperating head (15), and said operative position where it extendstransversely with respect to the longitudinal axis (x-x).
 3. Instrumentaccording to claim 2, characterized in that a pin (35) is integral withsaid widened proximal portion (28), perpendicular thereto, and ismovable inside a guide slot (35) formed in the stem (40).
 4. Instrumentaccording to claim 3, characterized in that said operating head (15) hasan essentially cylindrical shape and comprises a circular-rim guide (18)inside which said cutting element (30) is movably guided.
 5. Instrumentaccording to claim 4, characterized in that the distal portion (39) ofthe operating head (15) is slightly concave and said end tip (16) has afrustoconical form with a base diameter smaller than the diameter of theoperating head and projecting coaxially with the longitudinal axis (x-x)from said distal portion (39).
 6. Instrument according to claim 1,characterized in that a resilient element (34) which constantly biasesthe operating head (15) and the stem (40) away from each other and saidcutting element (30) towards said rest position is arranged between theoperating head (15) and the stem (40).
 7. Instrument according to claim3, characterized in that the cutting element (30) is formed integrallywith the pin (35) and projects from the matching seat (18) formed in theoperating head (15) under the pushing force of the distal end (38) ofthe stem (40).
 8. Instrument according to claim 1, characterized in thatsaid side opening (27) in said end tip (16) is an opening extendingalong the entire longitudinal extension of said end tip (16). 9.Instrument according to claim 1, characterized in that it comprises aguide pin (35) projecting laterally and perpendicularly from saidcutting element (30) and slidable inside a guide slot (33) formed at thedistal end of the stem (40).
 10. Instrument according to claim 1,characterized in that said pushing mechanism comprises the distal end(38) of said stem (40) and a pin (35) associated with said cuttingelement (30); said distal end (38) acting on the pin when the stem (40)is moved towards the operating head (15).
 11. Instrument according toclaim 10, characterized in that said approach movement of the stem (40)is performed against the action of resilient means (34).
 12. Instrumentaccording to claim 11, characterized in that the distal end (38) of thestem (40) has a circular cross-section and diameter smaller than theinternal diameter of the operating head (40) and that the spring-loadedmeans (34) consist of a spring wound around the distal end (38) of thestem (40).
 13. Instrument according to claim 12, characterized in thatthe spring extends resiliently inside a variable-extension, cylindrical,annular gap which is defined between an inner edge of the operating headand an edge formed by the smaller diameter of the distal end of thestem.
 14. Instrument according to claim 1, characterized in that saidcutting element (30) is curved essentially in the form of a circle arc.15. Method for the removal of a bone insert, for example for a shoulderprosthesis, of the type comprising the steps of: forming a hole ofpredefined diameter inside a bone portion from which said insert is tobe removed; inserting inside said hole an operating end of an instrumentprovided with a cutting element; said cutting element being movablyguided from a rest position, where it is concealingly housed inside saidend, to an operative position, where it projects through a side openingin said end, transversely with respect to a longitudinal axis of theinstrument; deep-cutting a base of said insert by pushing and rotatingsaid instrument through 360 degrees; removing the instrument from saidhole; inserting and fixing a pin element inside said hole; perimetrallymilling an insert of predefined diameter by centering a milling cutteron said pin element; removing the insert and the pin element attachedthereto.
 16. Method according to claim 15, wherein a flange is integralwith said pin and removal of the insert is performed by means ofengagement with said flange.
 17. Method according to claim 15, whereinsaid operative end of said instrument is a frustoconical portion of alarger-diameter operating head housing a pushing mechanism for adjustingthe amount by which said cutting element projects.
 18. Method accordingto claim 15, wherein said hole has a frustoconical form matching saidoperating end.
 19. Method according to claim 15, wherein said boneportion in which said hole is formed is flattened or made concavebeforehand or afterwards so as to receive a flat or convex flange fromwhich said pin projects.
 20. Method according to claim 15, wherein saidpin is perimetrally threaded or partially threaded.
 21. Method accordingto claim 15, wherein said pin is hollow.
 22. Method according to claim16, wherein the insert milling step is performed by means of a circularmilling cutter circumscribing said flange.
 23. Method according to claim21, wherein the milling step is performed by centering the millingcutter on a guide rod inserted inside the cavity of said pin.
 24. Methodaccording to claim 15, wherein said cutting element is made to projectonly when said operating end is completely inserted inside said hole.25. Method according to claim 15, wherein said pin is attached to ashoulder prosthesis portion.